The present invention relates generally to a knee joint prosthesis which replaces the articulating surfaces of the femur and tibia, and more particularly, to a prosthetic replacement system for a knee having interchangeable femoral and tibial components.
A knee joint prosthesis typically comprises a femoral component and a tibial component. The femoral component and tibial component are designed to be surgically attached to the distal end of the femur and proximal end of the tibia respectively. The femoral component is further designed to cooperate with the tibial component in simulating the articulating motion of an anatomical knee joint.
Motion of a natural knee is kinematically complex. During a relatively broad range of flexion and extension, the articular surfaces of a natural knee experience rotation, medial and lateral angulation, translation in the sagittal plane, rollback and sliding. Knee joint prostheses, in combination with ligaments and muscles, attempt to duplicate natural knee motion as well as absorb and control forces generated during the range of flexion. Depending on the degree of damage or deterioration of the knee tendons and ligaments, however, it may be necessary for a knee joint prosthesis to limit one or more of these motions in order to provide adequate stability.
While knee joint prostheses are effective in replacing the anatomical knee joint, they nevertheless have several disadvantages. For example, surgeons tend to select the size of the knee joint prosthesis by determining which knee joint prosthesis most closely matches the size of both the femur and tibia collectively rather than the size of the femur and tibia individually. This is because knee joint prostheses often lack interchangeability between various sized femoral components and various sized tibial components. Accordingly, the surgeon could not optimally select the size of the tibial component based primarily on the size of the tibia, as well as select the size of the femoral component based primarily on the size of the femur, so as to obtain the best anatomical fit for the prosthesis. In addition, knee joint prostheses sometimes lack interchangeability between a femoral component designed specifically for a right knee or a left knee and a particular tibial component.
In addition, knee joint prostheses often do not reproduce the relatively unconstrained kinematics of the anatomical knee joint. This includes translation of the femoral component in the sagittal plane with respect to the tibial component. Furthermore, such knee joint prostheses often do not permit the extensor moment arm between the patellar ligament and the femoral/tibial contact point to be taken into consideration during the design of a prosthesis. As a result, a noticeable change in the effort required by a patient during movement of the knee joint occurs when a prosthetic knee is compared with the natural knee.
Accordingly, it is desired to provide a knee joint prosthesis which substantially duplicates the motion associated with the anatomical knee joint while providing interchangeability between components.